A fuel supply system including a fuel storage tank in addition to a fuel pump and a regulator to serve as a reservoir as well has been used in a fuel supply channel extending from a fuel tank to an engine, in order to achieve stable fuel supply without interruption, even when a sudden acceleration or deceleration occurs during supplying liquid fuel stored in a fuel tank to the engine.
A known example of such a fuel supply system is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2008-297941 in which a fuel supply system includes a fuel pump that pneumatically supplies fuel stored in a fuel storage tank, which serves as a reservoir tank as well, toward the engine, a fuel storage volume adjusting unit having a float that maintains the liquid surface of the stored fuel at a predetermined level, and a regulator as a fuel pressure adjusting unit. The fuel that has become excessive by regulating the pressure is made to flow downward to the fuel storage tank from a return port formed under the regulator.
However, the downflow of the excess fuel disturbs the liquid surface of the stored fuel and moves the float. This impedes fixing of the stored fuel level and eventually prevents stable supply of fuel to the engine. Meanwhile, the fuel storage tank of the fuel supply system typically includes a function to deposit and remove moisture or foreign matters in the fuel. If the excess fuel flows downward from the regulator, the foreign matters deposited on the bottom of the fuel storage tank would be diffused in the stored fuel and conveyed directly to the engine.
To address these problems, the applicant of the present invention has previously proposed, in Japanese Patent Application Laid-Open Publication No. 2016-205169, a regulator holding member disposed over a fuel storage tank, in which an excess fuel discharge channel is formed extending from a recess that receives the regulator to an inner wall surface of the fuel storage tank. Excess fuel is returned through the excess fuel discharge channel. This enables stabilization of the level of the stored fuel, while avoiding the disturbance of the liquid surface of the stored fuel, thus eliminating adverse effects generated in association with the downflow of the excess fuel.
Meanwhile, the fuel supply system developed heretofore may include the regulator holding member described above, and may also have an open space above the fuel storage tank opened toward the upper space of the housing. This causes the adverse effects mentioned above associated with the downflow of the excess fuel. In addition, if the liquid surface of the fuel changes significantly by a vibration applied externally, the fuel would move up and down in the housing. Such up and down movement may also change the stored fuel level, making the stable fuel supply be further difficult. In addition, the movement of the fuel in the upper space of the housing would cause external leakage of the fuel through a path such as an atmosphere communication path.
In addition, a large movement of the liquid surface of the fuel by the vibration, as well as the vibration itself, would cause breakage or dropping of the harness and the joint portion of the fuel pump, leading to failure of operation of the fuel supply system. Therefore, it has been desired to develop a fuel supply system that can achieve stable fuel supply while minimizing the adverse effect associated with the vibration applied to the system, as well as the adverse effect associated with the downflow of the excess fuel.